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Zhenyang Cai Daxu Zhang Xinxiang Chen Yuntong Huang Yuqing Peng Canhui Xu Siyu Huang Rong Pu Sainan Liu Xiaojun Zhao Lairong Xiao 《Journal of the European Ceramic Society》2019,39(7):2277-2286
To protect refractory metal against oxidation at ultra-high temperatures, a MoSi2-TaSi2 ceramic coating was prepared on a pure tantalum (Ta) substrate using a novel three-step process, which included dip-coating with a molybdenum slurry, vacuum sintering, and halide-activated pack cementation (HAPC). The original coating had a MoSi2-TaSi2 double-layer structure from the surface to the substrate. After oxidation at 1700°C for 8 h in air, the coating exhibited a complex multi-layer structure composed of SiO2-Mo5Si3-MoSi2-(Mo,Ta)5Si3-TaSi2-Ta5Si3 from the outer layer to the inner layer, due to the high-temperature phase transition and diffusion of Si and O. The coating effectively protected the Ta substrate at 1700°C for 12 h without failure, thereby demonstrating great improvement to its service life in an ultra-high-temperature aerobic environment. The protective effect was attributed to the integrity of the ceramic coating and the formation of a dense, uniform SiO2 film that effectively lowered the inward oxygen diffusion rate. 相似文献
86.
Nitrile rubber (NBR) blends with excellent performance have always been a hot research topic in petroleum field. Due to the excellent performance and compatibility of polyamide 6 (PA6), it provides an opportunity for the preparation of high-performance NBR/PA6 blends. In this article, NBR/PA6 blends were prepared by the three-step molding process. Experimentally, it was found that PA6 has a prominent reinforcement effect in NBR matrix. The variation of this mechanical property was investigated from different aspects of the crystal structure, crystallinities, phase morphology, and so on. It can be cleared that the formation of fibrous structure of PA6 phase is the main factor for reinforcement of the polymer blends. Meanwhile, the formation mechanism of the special phase structure induced by the three-step process is deeply expounded and its structural evolution schematic is established. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47472. 相似文献
87.
Xiao-Dong Zhang Wen-Lu Zhang Ze-Xing Cai Yuan-Kai Li Yusuke Yamauchi Xin Guo 《Ceramics International》2019,45(5):5240-5248
LaFeO3 micro-spindles with intriguing structural characteristics were synthesized using cyano-bridged coordination polymers as sacrificial templates. Within a longitudinal dimension of less than 5?µm, each micro-spindle features a hollow center contained in a mesoporous shell with hexagonal cross section. Conductometric gas sensors developed from these micro-spindles demonstrate a comprehensively improved NO2-sensing performance over other-reported LaFeO3 devices, including lower operating temperature (155?°C), higher sensitivity (response of 81.4% under 5?ppm) and expedited response and recovery (40?s/329?s). Such performance is enabled by a semiconducting mechanism governed by the formation and catalytic dissociation of nitrite species during NO2 adsorption on LaFeO3, facilitated by the special hierarchical structure of the micro-spindle. 相似文献
88.
Xiaolong Cai Chenglin Du Zixuan Sun Ran Ye Haijun Liu Yu Zhang Xiangyang Duan Hai Lu 《半导体学报》2021,42(5):37-48
Gallium nitride (GaN)-based high-electron mobility transistors (HEMTs) are widely used in high power and high frequency application fields,due to the outstanding physical and chemical properties of the GaN material.However,GaN HEMTs suffer from degradations and even failures during practical applications,making physical analyses of post-failure devices extremely significant for reliability improvements and further device optimizations.In this paper,common physical characterization techniques for post failure analyses are introduced,several failure mechanisms and corresponding failure phenomena are reviewed and summarized,and finally device optimization methods are discussed. 相似文献
89.
Huizhu Cai Bingbing Chen Xiao Zhang Yuchen Deng Dequan Xiao Ding Ma Chuan Shi 《Nano Research》2021,14(1):122-130
Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe3C/C and Fe2N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH4/H2and pure NH3,respectively.By acid leaching of Fe2N/C sample,only single sites of FeN4species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN4in ORR.A correlation was conducted between the concentration of FeⅡN4in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin FeⅡN4 species as highly active sites for the ORR. 相似文献